John B. King Jr.'s tenure as head of the state Education Department wasn't perfect, but he was an impassioned advocate for higher standards and better education, and he will be missed.

Himself a founder and former principal of a very successful charter school in Massachusetts, King spoke out in favor of giving these independent public schools the chance to innovate and the tools to succeed. This has been crucial in moving education policy forward.

King announced Wednesday that he will leave at the end of the month to become federal Education Secretary Arne Duncan's No. 2. In an interesting side note on Washington politics, he will be called a senior adviser rather than deputy secretary because it's so difficult in this partisan Congress to get appointees confirmed.

King, 39, was in charge of implementing Common Core standards and a new teacher evaluation system in New York State. That put him in the crosshairs of angry educators who opposed tying their evaluations to student performance on standardized tests, and really, to any quantifiable measures.

Parents worried, too, that tougher standards and lower test scores were defining their kids as failures. A rollout in which King overpromised help with lesson plans and underdelivered made matters worse. Many educators now say the materials are quite good, but work on them should have begun earlier. The backlash culminated in Stop Common Core, a new ballot line in November's election, but much of the furor over Common Core now appears to have faded. Teachers, students and parents seem to have reached a comfort level with new methods and standards.

Under fire, King maintained composure and focus. In trying to improve New York City's schools, his successor will face a tremendous challenge. The politics are horrendous, the teachers unions are often intractable and the socioeconomic challenges many students face can be daunting. We hope his replacement continues the progress, and shows as much resolve in fighting for change, standards and students. And we hope King can continue his success on a national level.